Operator&#39;s telephone circuit



June 25, 1929. s, F NE| 5ON 1,718,301

OPERATOR S TELEPHONE C IRCUIT Filed Nov. l5, 1927 Cord Ending -W Cet.

frzdactance COLZ INVENTOR. 51 ZV1/maw BY A TT ORNEY Patented .inne 25, 1929. I

iii-nrs STATES PATENT OFFICE.

STANLEY F. NELSON, OF BRDKLYN, YORK, ASSIGNOR T0 AMERICAN TELEPHONE AND TELEGRAIH COMATY, A CORPORATION OF NEW YORK.

OPERATORE TELEHONE CIRCUT.

Application. filed November 15, 1927. Serial No. 233,414.

This invention relates to telephone systems, and more particularly to operators telephone circuits.

In telephone systems in lwhich two subscribers lilies are linked together through an intermediate circuit across which thereL is bridged an operators telephone set, itis important, particularly in cases of long distance transmission, that there be provided transmission of a. high grade for the operator. In one or more of the modern methods of toll line transmission a toll operator talks forward while the calling subscriber is connected to the line. vWith the arrangements employed at the present time, the transmission from the operator to the distant operator and to the called subscriber is impaired by the shunting effect of the calling subscribers line. Furthermore, while the operator is lining up the subscribers so that they may talk to each other, the transmission between the subscribers is impaired by the shunt of the operators telephone set. Vith the present type ol operators circuit, half of the output energy of the operators transmitter is absorbed in a balancing network; of the remaining half of the energy which reaches the transmission line, approximately one-half goes to the calling subscriber and one-half towards the distant operator and the called subscriber. Thus, it is seen that only about one-quarter oit the energy from the operators transmitter is projected towards the dista-ntfl'ioint, a serious transmis-- sion loss being involved.

The principal object of this invention an improved distribution in systems such as that discussed above of the output energy from the operatorls transmitter.

A further object ot the invention is an improvement of the transmission between the operator and the called line without an accompanying impairment ot the transmission over theL calling line.

In accomplishing the iirst object stated above, the applicant introduces into the operators telephone circuit an inequality transformer, arranged as will be more fully described below. I y

In accomplishing the second object stated above, the applicant introduces an additional feature into the operators circuit whereby the operators transmitting circuit is connected to the line only while the operator is talking, as will be more :tully disclosed below.

The invention will be better understood when the following detailed description is read with reference to thc accompanying drawing.

Figure l of the drawing shows diagran'imatically, and in part schematically, the applicants arrangement whereby a large portion of the operators transmitter energy goes to the toll line and the called subscriber while only a small portion of the energy goes to the calling subscriber.

Fig; 2 ot the drawing shows diagraminat-ically a modiiied arrangement whereby the operators transmitting circuit is connected to the line only while the operator is talking'.

With reference, first, to the details of Fig. l ot'the drawing, a calling line at the lett maybe connected to a called line at the right through an intermediate circuit including a so-called listening key. This listening key is designed to connect across the transmission line the operators telephone apparatus, which may take the form ot any suit-able operators telephone set. The applicant provides an inequality transformer, as shown, having' its low winding adapted to be connected to the calling line when the listening key is operated, and its high winding, which is directly in circuit with the operators telephone set, connected to the called line. lVith this arrangement, when the operator operates the listening key and talks, a largeportimi ot' the energy from her transmitter will go to the called line, where it is needed, andv only a small portion of this energy will go tothe calling line, this low energy being sutiicient since the line loss between the operator and the calling subscriber is, of course, quite small. The distribution otenergy is, of course, determined by the impedance ratio of the transformer windings, and accordingly, may be adjusted as is desired.

With the arrangement shown in Fig. l and described above, the traiismission between the operator and the called line is materially improved; the calling line transmission, however, as will be readily understood, is somewhat impaired. It it is desired to overcome the disadvantage oi low transmission efficiency for the calling line, the arrangement shown in Fig. 2 of the drawing may be employed. The principal feature which is added in this arrangement of Fig. 2 consists of a voice operated switching device which connects the operators transmitting circuit to the transmission line only while the operator is talking, the transmitting circuit being disconnected from the transmission line at all other times.Y

Fig. 2, like Fig. l, shows a calling line, a called line, an intermediate circuit designed to be connected to the calling line and the called line to link them together, and a listening key associated with the intermediate circuit. The operators telephone apparatus includes "the transmitter T and the receiver R. 7hen the listening key is operated, the receiver R is bridged directly across the intermediate circuit. If a high impedance receiver is used, no other apparatus will be required in the receiving circuit. If, however, the receiver R is not of the high impedance type, it may be necessary to include a monitoring` device, as indicated in the drawing, this device taking the form, for in.- stance, of a repeater.

Associated with the transmitter T is an inequality transformer having four windings 71, 72, 73 and 74. The winding 7l is in circuit with the transmitter. The windings 73 and 7A1 are designed to be connected across theicalling line and the called line, respectively. 7inding 73 has a relatively lowl number of turns, and winding 7., has a relatively high number of turns.

The winding V72 of the transformer is connected in circuit with a battery and the grid of a vacuum tube V, which is designed to function as a detector. lIn the plate circuit of the vacuum tube is the winding of a relay R, 7 hen the operator talks into the transmitter T, the grid of the tube V is made sutliciently positive to permit a flow of current in the plate circuit through the winding of relay R1. A relay R3 has its winding adapted to be connected through an inductancecoil and a battery. This inductance coil, however, is normally short-circuited.v Upon operation lof relay Bm the yshort-circuit of thel inductance coil is recalling line andthe winding 74 across the Y called line. Thus, the transformer T, which is normally disconnected from the transmission line, is connected in response to the operators speech to the calling line through a transformer winding which is relatively low and to the called line through a winding which is relatively high. The inductance coil described above functions to producea speedy operation of relay R3, and the slow release feature of relay R2 serves to maintain this operated condition temporarily.

7ith the arrangementV just described, it will readily be understood that the operators receiving circuit introduces only a negligible loss in thc transmission circuit, and that normally the operators transmitting circuit cannot introduce any loss since it is disconnected from the transmission line. 7hile the operator is lining up the two subscribers or is connected to the line for any other purpose, the transmission between the calling line and thecalled line is not appreciably impaired.

While the invention has been described specifically for the purpose of illustration, it is to be understood that it is capable of embodiment in other forms vdilferent from that disclosed within the true scope of the invention as defined in the appended claims.

7hat is claimed is:

l. In a telephone system, a calling line, a called line, an intermediate circuit adapted to be connected to'said lines to link them t0- gether, operators telephone apparatus, a transformer having a relatively low winding and a relatively'high winding, and a switch in said intermediate circuit for connectin 0 the low` winding of said transformer to said calling line and the high winding of said transformer to said called line and said operators telephone apparatus.

2. In a telephone system, a calling line, a called line, an intermediate circuit adapted to be connected to said lines to link them together, an operator-s telephone receiver, an operators telephone transmitter, means for connecting said receiver directly across said intermediate circuit, a transformer having a relatively low 'winding and a relatively high winding, and means operable only in re-V sponse to the operation Vof said transmitter for connecting said transmitter to said calling line through the low windingof said transformer and to said called line through the high winding of said transformer.

In testimony whereof have signed inv4 name to this specification this 14th day llovember, 1927.

STANLEY r. NsLsoN.

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